1. Field of the Invention
The present invention relates to a system for controlling the flow of air entering the intake manifold of a multicylinder variable displacement internal combustion engine installed in a vehicle having a driver operable accelerator control
2. Terminology
This is used herein to mean the volume of air admitted in cylinders of an engine per minute when the engine operates at an engine speed with a throttle disposed held in wide open throttle (WOT) position. The maximum air induction varies as the engine speed varies. Thus, a lookup table is used to provide an appropriate value of the maximum air induction at a given engine speed. In the description, the reference character xe2x80x9cMAXTPxe2x80x9d is used to represent the xe2x80x9cmaximum air inductionxe2x80x9d.
This is used herein to mean the volume swept out in one stroke by a piston in a cylinder. xe2x80x9cCylinder displacementxe2x80x9d is a synonym.
This is used herein to mean the sum of displacement of each of cylinders of an engine. xe2x80x9cEngine displacementxe2x80x9d and xe2x80x9cdisplacement of an enginexe2x80x9d are synonyms. In the description, the reference character xe2x80x9cVOL#xe2x80x9d is used to represent the xe2x80x9cengine displacementxe2x80x9d.
This is used herein to mean a ratio between the volumetric airflow admitted to activated ones of cylinders of an engine through a given effective flow cross sectional area and the maximum volumetric airflow admitted to all of the cylinders of the engine through the maximum effective flow cross sectional area. The maximum effective flow cross sectional area is provided when all the cylinder of the engine are in operation and a throttle in an intake manifold is WOT position. In the description, the reference character xe2x80x9cTQHOSTxe2x80x9d is used to represent the xe2x80x9cvolumetric airflow ratioxe2x80x9d and this ratio is expressed in terms of percentage (%).
This is used herein to mean a target value of a base volume of airflow entering the engine and can be expressed as the product of (xe2x80x9cvolumetric airflow ratioxe2x80x9d)xc3x97(xe2x80x9cmaximum air inductionxe2x80x9d). In the description, the reference character xe2x80x9cTTPSTxe2x80x9d is used to represent the xe2x80x9ctarget base airflowxe2x80x9d.
This is used herein to mean hardware and/or software used to operate a throttle or an exhaust gas recirculation (EGR) control valve or each of cylinders of an engine. For example, xe2x80x9cthrottle operatorxe2x80x9d is used herein to mean an actuator, such as a stepper motor, and its associated software for operating a throttle. xe2x80x9cEGR operatorxe2x80x9d is used herein to mean an actuator, such as a stepper motor, and its associated software for operating an EGR control valve. xe2x80x9cEngine cylinder operatorxe2x80x9d is used herein to mean hardware and software for deactivating and reactivating a cylinder and/or for varying strokes in a cycle.
3. Description of Related Art
Automotive designers and manufactures have realized for years that it is possible to obtain increased fuel efficiency if an engine can be operated on less than the full complement of cylinders during certain running condition and/or it can be operated on increased number of strokes in a cycle, Accordingly, it is possible to save fuel if the engine can be run on four instead of eight cylinders or three instead of six cylinders or two instead of four cylinders. Further, it is possible to save fuel if the engine an be run on eight-stroke or sixteen-stroke cycle instead of four-stroke cycle. Unfortunately, the engines of the above kind suffered from deficiencies associated with their control strategies. Specifically, the amount of air entering the engine per two crankshaft revolutions corresponding to a given accelerator pedal position at a given engine speed varied quiet widely with the number of activated cylinders and/or the number of strokes in a cycle of the activated cylinders. Referring to FIG. 8, for example, when the engine is in full-cylinder operation in 4-stroke cycle mode, there are four (4) induction stroke events in two crankshaft revolutions. However, when the engine is in 8-stroke cycle mode, there are two (2) induction stroke events in two crankshaft revolutions. Further, when the engine is in 16-stroke cycle mode, each of the cylinders performs induction stroke in eight crankshaft revolutions. This means that there is one induction stroke event in two crankshaft revolutions. Thus, a need remains to determine, with increased accuracy, the volume of air entering cylinders of an engine against varying operation modes of the engine.
The present invention aims at providing, with increased accuracy, a parameter indicating volume airflow ratio against varying operation modes of the engine.
It is an object of the present invention to provide a control system for an internal combustion engine, which has implemented the above-mentioned technique.
According to one aspect of the present invention, there is provided a control system for an internal combustion engine having a plurality of cylinders, comprising:
engine cylinder operator means for varying displacement of the engine cylinders;
means generating a cross sectional area against a given throttle position out of stored various cross sectional areas against various throttle positions;
means for determining an effective flow cross sectional area as a predetermined function of said cross sectional area;
means for generating a volumetric airflow ratio corresponding to said effective flow cross sectional area; and
means for modifying said predetermined function in response to a change in displacement of the engine cylinders.
According to a specific aspect of the present invention, there of provided a control system for an internal combustion engine having a plurality of cylinders, comprising:
engine cylinder operator means for deactivating and reactivating the engine cylinders and varying the number of strokes in a cycle; and
a control unit connected with said engine cylinder operator means,
said control unit generating a cross sectional area against a given throttle position out of stored various cross sectional areas against various throttle positions;
said control unit determining an effective flow cross sectional area as a predetermined function of said cross sectional area;
said control unit generating an airflow command corresponding to said effective flow cross sectional area; and
said control unit modifying said predetermined function in response to the number of engine cylinders being activated and the number of strokes in cycle.
If all of the engine cylinders are being activated with strokes in the standard cycle, the predetermined function is expressed such that the effective flow cross sectional area is equivalent to the cross sectional area divided by the total of displacements of the engine cylinders and also by engine speed.